i know this is a n00bish question, but what does it mean when a topic is "pinned"?

When a topic is relevant enough that everyone should/would want to read it, it gets pinned to the top of the list. Notice the first three to five topics on a board? Those are pinned. Most people look right over them after they have read them once.

The articles that say Pinned in front of them, like the two in the question center. They remain at the top no matter when they were last posted in.

-WarMan v2

For example, pinned items are usually topics that would help a new driver get on his feet, one topic might tell them the rules, how to find loads. Another might be what to look for in a company. Just things like that, I'm sure you get the point.